[meteorite-list] Irons and fusion crusts

[Rob McCafferty]

--- "Gary K. Foote" <gary at webbers.com> wrote:

> Hi Phil,
> 
> I don't mean to split hairs, but what is the
> difference between a thermal alteration zone 
> and a fusion crust?  Is there a difference? Is not a
> fusion crust a thermal alteration 
> zone?
> 
> Gary
> 

Oh, no, no, no.

A fusion crust is formed by the melting of the very
outer layer, proper actual melting.
Thermal alteration is caused by the presence of heat
without actually causing melting. The best I can think
of as an example is car brake disks when they get too
hot. When they cool back down they have a blue tint.
This is thermal alteration and exists to some depth in
the disk, not just on the surface. This is important
because it's not actually melted, it's just the heat
has alterd the crystal structure.

RMcC


 
____________________________________________________________________________________
Sucker-punch spam with award-winning protection. 
Try the free Yahoo! Mail Beta.
http://advision.webevents.yahoo.com/mailbeta/features_spam.html